Answers

I'm not entirely sure that's going to work. You'll have to test it. I'm not where I can test right now.

Checking the headers will tell you if it was addressed to some address in one of your domains. You can use a test in the exceptions to exclude any address that does resolve, but I'm not sure if the "Inside the organization" excpeption will do that or if
it will need to be an explicit DL.

All replies

The transport rules will not suffice in this situation. Since you have an Edge role installed in your environment you are going to want to use the recipient filter agent on the Edge Transport Server. Using this agent you can block delivery to
any recipient that is not listed in your GAL. Here's more information:

For catch all or non-existent mailboxes you have to use the Edge Transport Server. This is because the recipients are resolved before the message passes through through the transport rules agent which would exist on the Hub Transport Server.

I'm not entirely sure that's going to work. You'll have to test it. I'm not where I can test right now.

Checking the headers will tell you if it was addressed to some address in one of your domains. You can use a test in the exceptions to exclude any address that does resolve, but I'm not sure if the "Inside the organization" excpeption will do that or if
it will need to be an explicit DL.

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